Re: Variable pitch prop
AeroStar Marine still make variable pitch props. They are not truly variable, rather they are two-speed props. They are a three-blade stainless prop that automatically shifts between high and low ratio depending on load. You select the high pitch to match the boat and the low pitch will be 6" less - e.g. a 21" prop will be 21" high and 15" low. There is an adjustment wheel on the hub that can be turned by hand (without tools) to adjust the sensitivity of the change point - at the extreme ends of the adjustment the prop will stay either in high or low!
The results are quite spectacular, launching a boat onto the plane like nothing else but the price is a little eye-watering. I had a Maxum 1900 SR3 fitted with a Mercruiser 4.3L MPI 220hp motor and Alpha drive. The standard 19" 4-blade Vensura prop would get the boat from 0-30mph in about 7.5 seconds. A 19" 5-blade High Five prop would knock half a second off that, at about 7.0 seconds but a 20" AeroStar would do it in 5.8 seconds, whilst hitting a higher top speed, running lower revs and getting about 0.5mpg better economy across the cruising range.
The obvious drawback is the cost but the blades were individually replaceable so repairs would be easy and, also, a spare set of blades takes up much less space on a small boat than a spare prop. The same could be achieved with a two-speed transmission and it seems odd that no-one makes one. Look through the prop section of the forum and there are no end of posts from owners who want more out of the hole performance but don't want to sacrifice top speed or fuel economy - simply not possible with a single fixed pitch prop. Whilst cost, again, would be an issue, surely this could at least be offset by being able to buy a more modestly powered boat. Most owners don't need absolute top speed and would be content with fast planing and good cruising economy - both achievable aims with the combination of a modestly sized motor and a two-speed / CVT transmission.